This invention relates to rotary actuators and more particularly, to a limited angle rotary actuator and to a means of increasing the torque output of a rotary actuator.
Rotary actuators are needed in many engineering applications, particularly in the automotive field. Rotary actuation is usually accomplished using a geared motor. There are numerous disadvantages in using geared motors such as the undesirable noise which is produced by the gears, the number of component parts required by such a motor leading to unreliability, the need for frequent servicing and the increase in axial length caused by the need of a transmission between the motor and the part to be rotated and added bulk.
Stepper motors provide an effective means for converting digital signals into precise mechanical rotary movement. Rotary movement in discrete steps allows precise control over moving parts. However, the use of a stepper motor to carry out a precise actuation of a rotatable part over a limited angle may be undesirable given the cost and complexity of stepper motors. Lack of torque is an additional problem in conventional stepper motors.
It is an object of the present invention to provide a low cost limited angle rotary actuator which does not require gearing and which avoids the use of a conventional stepper motor.
Accordingly, one aspect of the present invention provides a limited angle rotary actuator comprising: an arcuate stator mountable on a platform, the stator being of predetermined length and having a predetermined radius so as to define a limited angle of rotation, the stator having a plurality of poles along its arcuate length which are controllably energizable to alternate their polarity; and a rotor mountable on an element to be rotated at a position remote from the center of rotation of the element, the rotor comprising a number of magnetic poles.
Preferably, the rotor comprises a first and a second rotor, the stator being located between the two rotors.
Conveniently, the rotor or each rotor comprises a permanent magnet which is magnetized into strips of poles of alternate magnetic polarity.
Advantageously, the rotor or each rotor comprises a plurality of discrete permanent magnets having poles of alternate magnetic polarity.
Preferably, the rotor or each rotor is part of an element to be rotated and is located at a position remote from the center of rotation of the element.
Conveniently, the stator is mounted to a fixed platform.
Advantageously, the stator is energizable to provide alternating poles in accordance with a conventional 2 or 4 phase energization sequence.
Preferably, the pitch of the poles of the rotor or each rotor is defined by the desired step angle.
Conveniently, the poles of the rotor or each respective rotor are located radially adjacent the poles of the stator, the profiles of the stator and the adjacent surface of the rotor or each respective rotor conforming with one another to minimize any air gap.
Advantageously, the stator has a first set of poles on one side of the stator, which side extends between the stator inner radius and the stator outer radius, and a second set of poles on an opposite side of the stator, which side extends between the stator inner radius and the stator outer radius.
Preferably, the poles of the stator are multipolar claw type stator poles.
Conveniently, the poles of the rotor or each respective rotor are located immediately adjacent the sides of the stator carrying the stator poles, the profiles of the sides of the stator and the adjacent surface of the rotor or each respective rotor conforming with one another to minimize any air gap.
Advantageously, the stator comprises a pair of stators.
Preferably, the stator or each stator comprises an arcuate core provided with a winding and sandwiched between two arcuate stator plates carrying the stator poles.
Another aspect of the present invention provides a rotary actuator comprising: a rotor mountable on an element to be rotated, the rotor comprising a first and a second rotor each provided with a number of magnetic poles; and an arcuate stator mountable on a platform, the stator having a plurality of poles along its arcuate length which are controllably energizable to alternate their polarity and drive the rotor, wherein the stator is located between the first and the second rotors and the stator poles on one side of the stator are adjacent the poles of the first rotor and the stator poles on the other side of the stator are adjacent the poles of the second rotor.
The above and other objects, aspects, features and advantages of the invention will be more readily apparent from the description of the preferred embodiments thereof taken in conjunction with the accompanying drawings and appended claims.